1. Field of the Invention
The present invention relates to a thin film coil including two coil patterns turned spirally in parallel with each other, a method of manufacturing the same, a coil structure having the thin film coil, and a method of manufacturing the same.
2. Description of the Related Art
In recent years, in the information communication field and the like, a common mode choke coil is spread as a coil part for reducing noise in a high frequency band. For example, the common mode choke coil is used for preventing noise of a radio broadcast or the like from coming into a telephone line.
The common mode choke coil has a configuration that, mainly, a thin film coil is buried between two magnetic substrates via an insulating layer. The thin film coil is generally constructed by including a coil pattern turned spirally. Examples of known common mode choke coils are a common mode choke coil including a thin film coil having a double turn structure in which two coil patterns are wound in parallel with each other at the same level (refer to, for example, Japanese Patent Laid-open No. 2002-110423) and a common mode choke coil including a thin film coil having a stacked structure that two coil patterns are stacked in different levels (refer to, for example, Japanese Patent Laid-open No. 2003-133135).
To improve the operation characteristic of the common mode choke coil, for example, for the purpose of improving the differential transmission (balance transmission) characteristic, it is necessary to reduce the capacitance (floating capacitance) between turns of a thin film coil (coil patterns).
More concretely, the capacitance generally depends on the inductance of the thin film coil. Consequently, when relatively large capacitance is generated, the capacitance becomes dominant in a high frequency band with respect to the impedance of the common mode choke coil. Therefore, when considering the fact that the impedance by the capacitance is inversely proportional to the frequency, as the capacitance increases, the impedance decreases and it causes deterioration in the differential transmission characteristic. It is consequently necessary to reduce the capacitance in order to improve the differential transmission characteristic.
However, in a conventional common mode choke coil, although it is necessary to reduce the capacitance as much as possible in order to improve the differential transmission characteristic, it is difficult to sufficiently reduce the capacitance mainly due to a structural factor of a thin film coil (coil patterns) and there is still room for improvement in reduction in the capacitance. Therefore, to improve the differential transmission characteristic of the common mode choke coil, it is urgently necessary to establish a technique capable of reducing the capacitance as much as possible. In the case of establishing a technique of this kind, it is particularly important that the common mode choke coil can be manufactured as easily as possible for mass production of the common mode choke coil.